oops,
First, when you upgrade the firmware when using ssh, just the one with .rar in the name, don’t use the one with .img. The .rar file is the correct one when you are in openwrt already. The one with .img in the name is used when flash using uboot webUI.
The uboot is not modified using pepe2k’s code, which doesn’t support nand.
What you could do is using uboot webUI: Debrick via Uboot - GL.iNet Docs
Press and hold the reset button when you power on. Just hold the button. The LEDs will flash once per second and after 5 seconds, LEDs will flash quickly and uboot web is ready.
Then flash the .img file according to the guide above. But many people report AR300M uboot web has a problem with windows. If you do, please use Linux or Mac